Origin of Universe

Introduction:

After studying the universe for more than 500 years, we still are not sure about its boundaries and existence of other life forms in it.
Starting with Nicolas Copernicus, the first person to observe the universe scientifically, to NASA and ISRO, we are still trying to unfold the mystery of the formation, expansion and limits of the universe.

Cosmology - the study of universe
The universe is almost 20 billion years old.
Universe is a possibly infinite space consisting of innumerable galaxies, planets, stars and maybe life forms.
Compared to the large dimensions of the universe, earth is just a speck of dust.
So, can we calculate the distance between earth and sun. It must be a very large number?
Enormous distances between the stellar bodies cannot be measured in the units of the metric system, it is measured in light years.
Light year - It is the distance traveled by light in vacuum in one year.
1 light year = 9.46 trillion Kilometers = 9.4 ˣ 10¹² Km
Thus when we look at the stars we are actually looking at the past.
We all know that objects can be seen when the reflected light enters the eye, as the light coming from stars started its journey millions of years back, traveled trillions of kilometers and reached us now, it is from the past.
Now the question that intrigues me is how did this universe, earth and life come into existence?
Several theories have been put forward to explain the origin of the universe, but the most acceptable one is the Big - Bang theory.

In 1931, a Belgian astronomer Abbe Lemaitre put forward a theory to explain the origin of the universe.
He stated that,20 billion years ago a huge explosion,unimaginable in physical terms took place.
It resulted in fragmentation and scattering of cosmic entities at a huge velocity making a bang sound.
Movement at high velocity leads to the expansion and cooling of space, resulting in formation of atoms.
These atoms later combined under gravitational force to form hydrogen and helium, further forming an infinite number of stars, galaxies and solar systems.
DO YOU KNOW - As per the latest data published in 2018 the estimated age of the universe is 13.7 billion years.

The Milky way is the galaxy in which our solar system lies.
4.5 - 5 billion years ago a gaseous cloud was formed in the galaxy, named as solar nebula.
The cloud eventually condensed as the temperature lowered.
Core of the cloud formed the sun while the periphery formed celestial bodies like planets, stars, satellites, etc forming the solar system.
The earth was formed 4.5 billion years ago,in steps-

i	In the process of condensation heavier elements accumulated in the center forming core, lighter ones formed mantle and the lightest formed the crust of earth.
ii	High energy cores lead to volcanic eruptions.
iii	Water vapor, methane, carbon dioxide and ammonia released from molten mass covered the earth
iv	Hydrogen and helium were the first gases to be formed
v	UV rays broke down water to release H₂ and O₂
vi	H₂ being lighter escaped
vii	O₂ combined with ammonia and methane to form water, CO₂, ozone etc.
viii	There was no atmosphere, no free oxygen thus the environment was reducing i.e breakdown of formed molecules was not possible
ix	Temperature lowered and water vapors precipitated to form oceans

1. Why was the theory for the origin of the universe named as the big bang theory?

Fred Hoyle, an english astronomer coined the term Big bang. A tiny dense mass exploded somewhere in the universe with enough energy to make a big boom sound. Hence the theory was named asThe Big Bang theory.

2. Why is the Big Bang is the most acceptable theory about the evolution of the universe?

Scientists have observed that several galaxies have been reported moving away from each other and from our galaxy, The Milky Way.The movement of galaxies seem like they are projecting because of an explosive force giving the basic idea of Big Bang Theory.

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